


Mundus: Mutata et Immutatus

by ImmortalBeing



Category: Shadowhunters (TV), The Mortal Instruments Series - Cassandra Clare
Genre: F/M, M/M
Language: English
Status: Completed
Published: 2020-10-24
Updated: 2020-10-24
Packaged: 2021-03-08 22:08:03
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 6
Words: 4,163
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27183592
Author URL: https://archiveofourown.org/users/ImmortalBeing/pseuds/ImmortalBeing
Summary: Alexander Lightwood loved a challenge so when he watched Magnus Bane sneak into a hidden corridor with Clary it was a no brainer to follow them, even after Jace did the same. Little did he know that one decision would lead to the world as he knew it being turned around, inverted if you would.Based off of Shadowhunters season 1 episode 10: This World Inverted. Alternate Alec ends up going through the portal and lands himself in the cannon world, but rather than taking over cannon Alec's body he remains in his own.All rights go to Cassandra Clare.Title is the best approximation of "The world: Changed and Unchanged" in Latin that i could get from Google translate
Relationships: Clary Fray/Jace Wayland, Magnus Bane/Alec Lightwood, Simon Lewis/Isabelle Lightwood
Comments: 2
Kudos: 14





	1. Chapter 1

"Playing hard to get?" Alec grinned, moving to go back to the party but keeping his gaze on the other man — Magnus Bane — for a moment longer. "I love a challenge." 

He socialized for a little bit, thoroughly enjoying the party he had painstakingly planned but never stopped thinking about the other man. These thoughts became even harder to ignore when he saw the man go into a hidden corridor with Clary. 

He hadn't known they knew each other but then again he didn't know anything about the man, yet. At least now he knew why the other was trying to get into the party but...that still didn't explain why they were going into a hidden corridor. 

He watched quietly as Jace followed behind them, no doubt angry. The blonde was like his brother and although he didn't say anything — in an attempt to not ruin the party — Alec noticed that he had been upset for the better part of the day. No doubt did Jace think Clary was cheating on him.

He supposed he would be upset too, if he didn't know any better. Whatever reason they had for going into the corridor was likely not the one Jace was thinking. Alec had more faith both in Clary and the man he had just met.

He waited, letting there be ample time for Jace and Clary to talk things out. 

After what he assumed was enough time passed Alec politely excused himself from the conversation he had only been half paying attention to and followed after them. 

It was clear there had been a fight, there were boxes strewn everywhere and- what the fuck was that? 

Okay. Something was weird here. Whatever was lying there did not belong. It seemed to be dead but who killed it? What the fuck- 

Alright. He was not going to get any answers just staring at the thing, whatever it was. He hurried down the corridor, only half paying attention to where he was going. He had to find the others. 

Just find them walking through some sort of purple door that he was certain wasn't there before. And Magnus was— what was he doing? There was blue coming from his hands—? 

Did he open the purple door? Where are Clary and Jace? 

He rushed forward, running at the purple door as he wondered what Magnus had done and why. 

Vaguely he was aware that the man had yelled out for him to stop but by then he was too late. Alec had gotten through the purple door.


	2. Chapter 2

He blinked in confusion at the building that he was in. A glance out the window showed that he was still in New York but there was no way this loft was inside the Institute. 

"Alexander? What are you doing here?" The Warlock asked as he walked into the room.

Alec's head snapped towards the voice, already recognizing it as Magnus' only to stare in confusion once more as he took in his appearance. It wasn't a bad change but it was certainly different than the outfit he was just wearing. 

"Magnus? What- where are we? What was that door?" He questioned, looking around the loft once more as if any amount of looking would clue him in to where he was.

Magnus gave him a look of concerned confusion, taking in what he said as well as how he was dressed for a moment before speaking again. "My apartment. You've been here before—" 

"Alexander. Are you alright?" Magnus asked, stepping closer to the other. 

"Yes, fine, but, where are Jace and Clary?" 

"I haven't seen them. Why would they be here?" 

"You sent them through that weird purple door. I followed them and ended up here."

"Weird purple door?" Magnus questioned. He knew the other meant a portal but he also knew Alec would have just called it a portal. 

Magnus stepped closer to the other, looking him up and down in search of any or the runes that were normally visible. Unsurprisingly there weren't any. 

Alec smiled as the other got closer. He was still confused but he wasn't going to complain if the man wanted to be close to him. "Already done playing hard to get?" He joked, moving even closer to him. 

If Magnus hadn't already been certain that this Alec wasn't his Alec those words solidified it. He placed his hand on NotAlec's chest and gently pushed him back. "You're not Alexander." 

"Yes I am—"

"Not the Alec of this dimension." 

"...what?" 

"Sit down, I'll explain." 

Alec did as he was told, nodding when he was asked if he wanted tea. A moment later his hands were hot and he looked down to find a cup of tea from Joe, the Art of Coffee. 

"How—?" 

"That 'weird purple door'." He quoted. "Was a portal. "Stepping through it must have led you here."

"So will another portal take me home?" Alec readily believed him simply because this Magnus seemed a lot different than the one he had met.

"It's not that simple. Portals in that world must work differently than portals here. We can't move between dimensions that easily." He paused, remembering what this Alec had said before. "Jace and Clary. You said they went through this portal as well?" 

"Yeah, they went in before I did." 

The Warlock nodded quietly as he connected the dots. The Jace and Clary the other saw were likely from the current world. Considering the necklace Clary had it made sense but he still wasn't certain how he was going to get Not-Alec back to his own world. 

This was a conundrum. 


	3. Chapter 3

"Jace! Jace! No. No."

They had just ran as fast as they could, through the city and into the seelie woods just to get to Jace but it was clear they hadn't been fast enough. 

He had watched in defeat as some sort of seelie door or portal closed, barring them from being able to follow Jace.

"What was that?" Lydia asked, seeming out of breathe despite her stamina rune. 

"I don't know but if they're in there, they're not coming out." Alec sighed. This was great, just great. He had weakened his parabati bond with Jace to find him and he hadn't even actually found the man. 

The bond was so weak it felt as if he was missing a large part of himself. He was doing what was needed to save his sister, and be would never regret that, but a part of Alex regretted how he chose to go about it. 

If he had acted differently—

"Hey-" Lydia interrupted his thoughts, placing a gentle hand on his shoulder. "We'll find them." Truth be told she wanted Isabelle free as much Alec did. But she _had_ to follow the rules. That's why she was here in the first place, after all. 

Alec nodded, not believing her but appreciating her efforts nonetheless. "We have to get back. Tell Izzy what happened." 

"Maybe there's another way we can help her?" She suggested as they started to head back towards the Institute.

He nodded. "If there is I will find it." 

Nothing mattered to Alec Lightwood more than family did. It was, after all, the exact reason he was marrying Lydia; to restore honor to his familiy name. For all of their sakes. He refused to let Izzy and Jace suffer, be it because if their choices or because of their parents' choices he would make sure all of them would be okay.

**Notes for the Chapter:**

> I know a lot of Malec fans hate or hated Lydia. I am definitely one of the ones who don't hate her. I was certainly upset my first watch through when Alec proposed to her but watching the whole thing, seeing her tell Alec it was okay in the wedding scene? Not to mention the fact that she genuinely cares about them? 
> 
> I love it and her she is a pure bean.
> 
> That being said this is still a Malec fanfiction but I have to keep things as canonical as I can, thus Lydia and Alec are still engaged as of right now.


	4. Chapter 4

Magnus opened the door, letting Alec into the apartment. The other Alec was still on the couch and Magnus didn't bother to hide him. He was going to need help getting him back to the right dimension anyways so why bother hiding him?

Alec took Magnus' silence as permission to speak. "I need to ask you somethi—" He choked on his words as he saw the other Alec on the couch. "Why am I on your couch?" 

"You came all the way to my apartment to ask me that?" Magnus couldn't help to fuck with the other. 

Not!Alec stood up, smiling at the Alec of this world. Magnus had already explained everything so he wasn't as suprised as the other Alec. "So you're the Alec lucky enough to be with this beautiful man?" He was assuming they were together from both his own attraction to the man and the way Magnus had moved closer to him earlier.

"What- no- I'm enagaed— Magnus, what is going on?" 

"He—" Magnus started.

"You two are engaged?" 

"No-!" 

"Alexander here is engaged to a woman. Something about honor, I believe?" Magnus stated cooly. His biggest issue here wasn't even how he felt about Alec, it was Alec's reasoning for marrying the woman. It was a political marriage, one in which Magnus knew Alec would not be happy and he didn't want that for the other man.

"What?" Not!Alec questioned, brows furrowed in confusion. The world he lived in was very different. He didn't have to worry about family honor or anything like that.

"I'm not here to talk about any of that. This is about my sister." Alec replied.

"Izzy? What's going on with Izzy?" Not!Alec was instantly concerned. He knew that technically the Izzy of this world wasn't his sister but he still wanted her to be safe. 

"Alec's adorable fiancée has Isabelle on trial for treason." Magnus answered, pouring himself a drink before sitting down. This was going to be a long day- 

"What-!?" Not!Alec was very confused. How was Izzy on trial for treason what did she even do?? They had to help her.

"I don't have time to explain everything right now." He said, looking at his double for a moment before looking back at Magnus. "My sister wants you to be her defense attorney. I said I would ask. Sorry for bothering you, I know a downworlder can't defend a Shadowhunter in court."

"But a Shadowhunter accused of a crime can choose _any_ advocate." 

"That can't mean a Downworlder." 

"The Clave was so rigid and prejudiced back in what they call the Time of Angels that they didn’t dream of a Shadowhunter asking a Downworlder for help. They didn’t even bother to exclude us. So, since, as you all say, 'the Law is the Law', there’s no stopping me from slipping through this gaping loophole. For the right price."

"Name it." Both Alecs said at the same time. 

Magnus and Alec looked over at Not!Alec in suprise, neither expecting him to speak. "The Isabelle of this dimension isn't actually your sister." Magnus pointed out. 

"I know but- she's still Izzy. Whether she's _my_ sister or _his_ sister I want her to— no, I need her to be okay." 

Alex nodded. "Family is the most important thing." 

"Always." 

Magnus sighed, a smile hiding on his face. At least the Alecs were realizing they weren't so different after all. Maybe there was so hope for them after all. "Fine, I'll help. But then you're going to help me return him to the right dimension." 

Normally he would have asked for something else, something that would show Alec's sister meant enough for him to make a real sacrifice but if there were two Alecs here than there was likely none in the other dimension. 

Based off of what Not!Alec had told him there was a big chance his other self was not having a good time. 

**Notes for the Chapter:**

> Still working on this!! I've just been writing bit by bit before work as I'm typically playing destiny 2 at home since the next season is in one week! 
> 
> I literally ran into this fic the other day and got excited by the summary before realizing it was my story   
> If I wanna read more I gotta write it so here we are xD


	5. Chapter 5

Close the portal. Clary had said. So no more demons could enter their dimension and hurt them. 

It had made sense, at the time, he had actually agreed with the plan. A demon coming to attack them when there was no one with any training would be the worst possible scenario.

At least, that's what Magnus had thought until Alec had walked through the portal right before he had finished closing it. 

He had tried to stop him but the other wasn't listening and had just walked right through. Magnus had no idea if he was even alive or not. Going through a portal without thinking of who you where going to could be disastrous. 

Best case scenario, he was thinking of Jace or Clary and was back up at the party where the Jace and Clary if this dimension were. It'd be a little confusing for him but he would be okay. 

Worst case scenario? He was lost in limbo with no way out. Even if he hadn't closed the portal Alec would still be trapped? 

He went to mindlessly cleaning up the demon, hoping that Alec was just upstairs. He knew if he was the other likely would have come back down, demanded answers. At least, that's what he would expect anyone to do. 

If he was gone? 

Magnus wasn't sure what he was going to do. Obviously he would try to find him but how would he even begin to explain it to everyone else? 

He wasn't even on the guest list but here he was because Alec had said he'd be responsible for him. 

He sighed, preparing himself to return to the party.

* * *

What-?

Jace blinked im confusion, looking around at the party. 

This was good. This was normal but...he had just been downstairs, about to piss himself because of a- because of whatever that thing was—

Was that a dream? But, no, he was standing here, in the party. How could he have been asleep? 

"Jace?" 

He looked to his side to see Clary, a wave of emotions hitting him. The same happiness he always felt when he was near her but also that sickening jealously. At least that other guy wasn't around. 

"Yes, Clary?" 

"How did we get here?" She looked around, confusion apparent on her face. "Last thing I remember I was in the kitchen and then...here we are."

Just like him, expect he went to the basement and then ended up here. Whatever happened to him must have happened to her too, even earlier than it happened to him. 

So she wasn't cheating on him? But then what was with that other guy? Did he have something to do with this? 

"I'm not sure," He spoke gently, reaching to push a lock of her hair behind her ear. "It must've been a long day." 

"Yeah-" Clary responded, clearly uncertain.

"How about we dance, and after the party we figure it out together?" He offered, holding out his hand.

She took it with a smile. "Yeah, that sounds nice."

* * *

Once Magnus was back upstairs he looked around, easily spotting Clary and Jace but not seeing Alec anywhere. Maybe he was somewhere else? He doubted it but he had to check. 

Besides, it wasn't as if he could pretend like he wasn't here. Even if no one else had paid any attention to him the bouncer certainly had. He couldn't pretend he hadn't been here or that he hadn't been with Alec.

He walked over to where Jace and Clary were dancing together, coming to stop by them and waiting for them to stop dancing before he spoke — he didn't want to interrupt the happy moment they were having any sooner than he had to. 

"Excuse me, have either of you seen Alec Lightwood? He helped be get in here but...now I can't find him." 

"Alec's missing?" Jace replied, expression quickly changing to a serious one. Alec was like his brother. He wasn't going waste any time messing around if he was missing. 

"Whoa-" Magnus held his hands up, wanting to calm Jace. Yes, he was pretty sure Alec was missing but he didn't want to jump the gun. "I never said that. Just that _I_ can't find him." He scanned the room with his eyes, both to further his point that he was looking and to actually look for him again. 

Clary quickly followed suit, only stopping once she confirmed that she also could not see the other. That was worrying. Alec had put his everything into planning this party. He wouldn't just leave.

"Something has to be wrong though, right?" She spoke as she looked at Jace, continuing when it seemed he wasn't sure. "You know how much he cared about this. Why else would he be gone?"

Jace nodded, pulling out his phone. "I'll call him. Maybe he's in the bathroom or something-?" He moved over to a quieter part of the room as he called Alec, gaze never leaving Magnus. 

Oh, right. Magnus had forgotten for a moment that this world's Jace had thought something was going on between him and Clary....and had seen the demon. Did he remember all of that—?

"I'm Clary." She said as Jace walked away, holding her hand out to shake his. She was unaware both that Magnus technically already knew that and that her boyfriend was eyeing them as hw called Alec.

"Magnus Bane." He shook her hand, despite Jace's staring. Avoiding it would be just as bad. Besides, if Jace did remember what happened before the other Jace took control then even if he said something it would ultimately be good. At least then things would be a little easier to explain. 

"He's not answering." Jace said with a frown when he rejoined them. He was upset that Magnus had touched Clary but he also understood that a handshake was a handshake. And he knew that to his Clary this was the first time they met. He couldn't be mad at her for being polite. 

"Could he still just be in the bathroom?" Magnus hopefully asked. 

"No, he would have at least texted me if he could, bathroom or not." Jace responded, still eyeing Magnus unhappily. 

"He was here earlier, right-?" She was still unsure since she couldn't remember anything from earlier but if he had let Magnus in to the party then Alec had to of been here. "He can't be far if something did happen?" 

"I don't know. Why don't we ask him." Jace gestured to Magnus. "What did you do to him." 

"What-?" Confusion laced Clary's voice. 

"I didn't hurt him-" Magnus looked around before looking back at Jace. "You remember earlier? With that thing?" 

Jace nodded, still not happy whatsoever. Alec was missing and he was sure this man was to blame. 

"Good. Let's go somewhere more quiet and I can explain everything I know."

"So you do know what happened to him?" Clary asked.

"Not exactly. I meant it when I said I couldn't find him."

"Follow me." Jace led them to a private room. Somewhere it was likely they wouldn't be interrupted. 

Once they were alone he looked over at the other man, crossing his arms as he spoke. "Explain."


	6. Chapter 6

"That 'thing' you saw earlier was a demon." Magnus started, not even bothering to try and ease Jace or Clary into it. He knew it would only make things worse for him. 

"Demons don't exist." Jace said simply. He was starting to believe that Magnus was crazy. That had to be the only reason, except...he didn't have any logical explanations for what he saw either- 

"You're right. They don't. Not anymore, at least. Demons have been extinct in this dimension for centuries." 

"What are you talking about? Demons?" Clary looked over at Jace. "What did you see? When—?" 

"When you were being controlled by the Clary of the other dimension." Magnus cut off anything Jace would have said. "She took control this morning, the Jace of her dimension took control of you," He gestured to Jace. "Shortly after you saw the demon." 

"Why?" Jace questioned.

"To protect Clary from the demon, I'm sure. It did come from their dimension, after all." 

"That explains why I can remember anything from today but why were they here? What were they doing?" Clary asked.

"In their dimension the war between shadowhunters and demons still wages on. That Clary said there was something much worse than demons that they were fighting and she needed my help to stop it." 

"What could be worse than that _thing_ I saw?" 

"I didn't ask. But it seemed important and she had a shard of the last standing portal in this dimension. With that I was able to fix the portal in the basement and send them off to where they needed to be." 

" _That's_ why you two snuck off into the basement?" 

"Yes. I may be a freewheeling bisexual but believe me when I say I have more interest in Alec than in either of you two." 

"Speaking of Alec. You still haven't explained what happened to him." 

"He came downstairs, whether after me or one of you two, well, I never got the chance to ask." 

"What do you mean?" Clary asked. 

"When he saw what he believed to be you two going through the portal he followed. A moment later the portal was closed." He grimaced, still upset that he had done that even though he knew he hadn't meant to.

"You closed him in!?" 

"That wasn't my intention and it wasn't as if I could help it either. I had already started closing it before he showed up. In order to prevent more demons from coming through. By the time he jumped in it was too late." 

"So he's stuck in a portal because of you and you have the audacity to come and ask us if we've seen him!?" That his brother! How dare Magnus do that to him-!

"The portal takes you to whoever you are thinking about at the moment. It could have been me or either of you two. Since he didn't appear next to me I was hoping he was with one of you." 

"But he wasn't so...where else could it have taken him?" Clary's brows were furrowed as she tried to figure out where Alec could be. 

"Anywhere, depending on who he was thinking of." 

"Or?" Jace pushed. 

"Or closing the portal could have malfunctioned, causing him to be in limbo regardless of who he was thinking of. Or he could be in the other dimension." 

"The one with the demons?" Clary paled at the realization that Alec was not only missing but likely in danger. 

Magnus nodded. "That's why I need your help to find him." 

"Why should we trust you?" Jace asked. "It's your fault he's missing." 

"Because I could have left. Pretended to never be here, pretending like I never even met the man but I stayed to help." 

"You couldn't leave anyways, someone had to have seen you. You're only here to save your-"

Magnus snapped, cutting Jace off as his fingertips light up with blue flame. "I'm a warlock. I possess magical abilities. I could have wiped the memories of everyone here had I chosen to do so. But I stayed."

Truth be told Magnus hadn't even considered doing that. It would too difficult to wipe everyone's memories without anyone realizing it but they didn't need to know that. He only needed them to trust him so that he could try to track Alec. If he was anywhere in this dimension Magnus was going to find him.

Both Jace and Clary's eyes widened at the show of magic. Despite hearing about demons and portals this was the first thing that made it real for Clary and the first thing that forced Jace to accept that what he had seen really was a demon. 

"Fine. But how do we help?" Jace asked. 

"I need something that belonged to him. Something I can use to track him. If he's still in this dimension I'll be able to find him."

"And if he isn't?" Clary asked.

"Then we'll have to think of something else. I won't stop until we find him." He paused. "It won't be long until someone else notices he's missing." 

Clary nodded. "You should leave, just in case. We'll figure out something."

"Meet me back at my place when you have something of his." Magnus left as he spoke, really not wanting to still be at the party when everyone else noticed he was gone. 

"Figure something out? How are we supposed to explain a missing person?" 

"I don't know Jace. But if we let Magnus take the fall for it we lose our only chance of finding him. We can't let that happen." 

He frowned. She was right but he still wasn't sure what he was going to say. How do they explain an entire missing person away without becoming suspects themselves? 

"We'll think of something, okay? For now let's just get back to the party before anyone worries about us as well."

"Yeah, we can finish our dance." He smiled as Clary lead him back to the party. 

They didn't get to start the dance however because Isabelle intercepted them. "Simon just asked me to move in with him!"

Clary grinned. "I'm so happy for you two!" 

"Thank you!" Isabelle looked around. "Have you two seen Alec? I want to tell him about this too."

**Notes for the Chapter:**

> For those who don't know Magnus calls himself a freewheeling bisexual in the books and I couldn't resist finding a place to use that same line xD


End file.
